Glossary of Terms

Cooling Mark - String-like inclusions in glass caused as the hot glass cools. Often called “straw marks.”

Sand Deposit - Small included piece of sand remaining from the manufacturing process. May look like bits of sand or a small stone.

Bubbles - Included Bubble - A bubble that is 100% below the surface of the glass
                 Seed Bubbles - Tiny included bubbles, usually found in clusters or throughout a piece

Sun Purple - When manufacturers produce glass, chemicals (clarifying agents) must be added to clarify the batch in order to turn it from its original color of aqua-blue or green to     clear. Prior to the start of the First World War, manufacturers used Manganese Dioxide as their chemical agent of choice to clarify glass. When a jar or bottle turns purple from sunlight, manganese dioxide is the substance in the glass that reacts with sunlight to cause the color change. Russia was the primary source of this chemical.

When the First World War broke out, our source of manganese dioxide was cut off by German blockades. This sudden loss left glass manufacturers in a quandary and forced them to use another chemical, selenium, to clarify glass. After the close of the war, manufacturers did not return to the use of manganese dioxide. Selenium does not cause glass to react to sunlight like manganese does, thus glass clarified with selenium does not turn purple. Knowing this fact and the history above, collectors have another way to date their glass collectibles. If your jar is purple, it is a pretty good bet it was made before World War I.

  Japanning - Is a metal finishing process that was often used on tools and other metal items around the turn of the century which produces a finish like a thick enamel paint coating.          There are different recipes but most consist of a combination of asphaltum, linseed oil and turpentine which is then baked on the metal.